@Time40
Good Grief. It's not like they are asking you to be there an HOUR before. It's just 20 minutes.
It is good 'Wedding Etiquette' to come 20-30 minutes before the actual ceremony.
I went to a wedding last year, and about 70 people were invited/due altogether. 60-ish came 25 to 35 minutes before the ceremony was due to start, and around 5 or 6 came only 2-3 minutes before, and they struggled to sit together.
As almost everyone was there, they looked uncomfortable and awkward, and a bit silly faffing about looking for somewhere to perch!
The remaining 4 or 5 came LATE. Only 5-7 minutes, but LATE. Luckily the bride was 10 minutes late (her prerogative!) The 4 or 5 LATE people looked like idiots. Inconsiderate, thoughtless idiots.
They struggled to find a seat, and expected people to move, and shift up all the seats so they could sit down/sit with their partner.
One woman would have been behind a big pillar if her party of 4 had moved up, so they all refused to budge, and one woman ended up standing throughout it all (as it was too late for the 'Church helpers' to go around looking for extra chairs in the parish hall next door.)
3 or 4 people had come who were not invited, and left the seating short. But if everyone had come early (no more 5 minutes before the time the ceremony was to start,) someone would have got them a chair from the Parish Hall next door.
They weren't about to start accommodating rude and inconsiderate individuals who couldn't be arsed to turn up until on time, and rocked up 5 to 7 minutes late. So rude.